This invention concerns the preparation of finely comminuted particles of a normally solid thermoplastic organic polymer. In one aspect, it concerns the preparation of such particles in a form where it constitutes a highly desirable toner for electrostatic reproduction processes. Still more particularly, the invention provides a unique toner composition which permits toner fixation by pressure fusion to give a matte finish copy. The invention will be described in conjunction with such toner, although the invention is applicable to a wide variety of other processes.
In the various processes of electrostatic reproduction (see "Reprography", in Kirk-Othmer's Encyclopedia of Chemical Technology, Vol 17, Second Edition), electrostatically charged particles of a pigmented toner are caused to adhere to an image on a sheet of paper or other substrate, and are then permanently fused (or fixed) onto the paper by the application of heat or pressure. The use of such toners in electrostatic reproduction processes is exemplified in, for example, Nelson U.S. Pat. No. 3,639,245, Kotz U.S. Pat. Nos. 3,816,840, Kotz U.S. Pat. No. 3,909,258, Strong U.S. Pat. No. 3,965,022, and Shely U.S. Pat. No. 3,563,734.
A particular problem arises when fusion is effected by pressure. While pressure fusion provides advantages from the standpoint of rapid trouble-free apparatus, it frequently results in a glossy copy, especially where there is an extensive black area on the print. Glossy prints are undesirable from the standpoint of the user, who frequently objects to the annoying reflections from overhead illumination.
The common technique of manufacturing toners in finely comminuted form by such procedures as fine grinding, micronizing, spray drying, or the like has thus far been unable to provide toners which give a matte, as distinguished from a glossy, appearance. It is theorized that particles of a pigment such as carbon black, when incorporated into such toners, are dispersed or suspended in the body of each polymer granule, and thus are unavailable at the copy surface after a toner has been pressure fused onto a substrate.
Accordingly, a primary object of the invention is to provide a toner for electrostatic reproduction processes utilizing pressure fusion as a fixation technique, which toner gives a matte finish copy.
Another object is to provide a unique process for preparing finely comminuted particles of a normally solid thermoplastic organic polymer.
Still another object is to provide finely comminuted particles of a normally solid organic thermoplastic polymer, where the particles or granules of the polymer contain carbon black dispersed in the body of the granules as well as carbon black as an adherent coating on the granules.